A fossilized dinosaur dropping collected on a Montana hillside a decade ago has yielded what researchers describe as the best-preserved fossil feathers known from the Mesozoic era, and it is pointing paleontologists toward a possible answer to one of the field's long-standing questions: why a single lineage of birds survived the asteroid impact 66 million years ago while their close relatives did not.

The findings were published on September 10 in Current Biology by a University of Washington-led team, with Jingmai O'Connor, associate curator of fossil reptiles at the Field Museum in Chicago, as lead author. The specimen came from the badland exposures of the Hell Creek Formation in eastern Montana, one of the most heavily worked Late Cretaceous fossil sites in North America.

The discovery matters beyond the novelty. It establishes coprolites, the technical term for fossilized dung, as a possible new place to look for delicate soft tissue that rarely survives in the rock record. "This means that coprolites are potentially a new window through which we can study fossilised soft tissues," O'Connor said.

A Rock Nobody Would Have Looked At Twice

David DeMar Jr., a University of Washington research scientist and the Hell Creek Project collections manager at the Burke Museum of Natural History and Culture, found it in 2016 while collecting fish fossils.

"I was crawling up a rocky outcrop collecting fish fossils when I came across a dark, reddish-brown nodule about half the size of a golf ball," DeMar said in the University of Washington's announcement of the discovery. "I picked it up and scanned its surface through my hand lens, and that's when I couldn't believe what I was seeing: a tiny fossil feather." He added that he was cautiously optimistic, because no feather had been found in the Hell Creek Formation after more than 100 years of prospecting.

The nodule had broken open at some point, leaving a feather exposed on the surface. Micro-computed tomography scanning, which stacks thousands of X-ray slices into a three-dimensional model, revealed the rest: multiple feathers, tiny fish scales from a gar, and leg bones from a small bird.

Nathan Carroll, a study co-author and paleontologist at the Carter County Museum in Ekalaka, Montana, described the scanning process. "Every hour processing the data revealed another feather, another scale, another bone, in stunning 3D," Carroll said, adding that finding such material in fossil dung from his home state changed how he thought about where exceptional specimens come from.

The bones identify the prey as a hesperornithiform, an extinct group of aquatic, flightless diving birds ecologically similar to modern loons. The researchers reasoned that the feathers came from the same animal. These are the first hesperornithiform feathers ever identified.

The dinosaur that produced the coprolite has not been identified. Based on its size and contents, the team considered Tyrannosaurus rex and Nanotyrannus as candidates, and the paper notes that the predator was probably opportunistic but that little more can be said without a more precise identification. O'Connor noted that the candidate dinosaurs were unlikely fish eaters, which led the team to a second inference. "We hypothesise that those tiny fish scales were in the stomach of the bird when the bird was consumed," she said. "So this coprolite actually records two different food web interactions."

Modern Wing, Primitive Body

The structural detail is what gives the specimen scientific weight. According to Sci. News, the feathers appear to sit at an evolutionary midpoint, combining forms associated with reduced water penetration in modern water birds with smaller, fuzzy, primitive feathers of the kind associated with dinosaurs.

"Two of the feathers, including the one exposed at the surface of the coprolite, have features found only in those of living birds, and their immediate ancestors," DeMar said. "This includes a square feather shaft with a sponge-like center. No other Mesozoic feather has this combination of features." He noted that the next oldest record of that sponge-like core comes from the early Eocene of Denmark, roughly 10 million years younger.

Gregory Wilson Mantilla, a University of Washington professor of biology, curator of vertebrate paleontology at the Burke Museum and leader of the Hell Creek Project, said fossil birds and especially their feathers are rarely recovered at all, and that finding them inside a large fossilized dropping opens an unusual window into predator and prey relationships at the end of the Cretaceous.

The Hypothesis, and Its Limits

The extinction explanation is a hypothesis the authors are proposing, not a settled conclusion.

Some paleontologists have suggested surviving birds made it through because they lived near water. Hesperornithiforms also lived near water, and they died out, which weakens that explanation. The new proposal is that plumage, or the way birds molted it, may have mattered.

"We think the types of feathers that these birds had, and/or the way they molted those feathers, may have been one of the underlying causes of the selectivity of the end-Cretaceous mass extinction, essentially, why some birds died out and why others survived," O'Connor said. She framed the insulation idea as something that can now be hypothesized, namely that only crown birds had the full combination of insulating body feathers and modern wing feathers.

An independent researcher not involved in the work found the preservation impressive but the inference unresolved. Steven Salisbury, a vertebrate paleontologist at the University of Queensland, told ABC News that most feather fossils are impressions rather than the feather itself. "This is cool because it's actually the preserved feather in 3D," he said.

On the extinction argument, Salisbury called the reasoning intriguing but incomplete. "One of the great mysteries of any extinction event, and in particular the Cretaceous extinction event, is why some groups of animals get through, and others don't," he said. "I don't think we know exactly what happened." He said more fossils are needed to test the team's idea.

That is the honest state of the evidence. This is a single specimen. It documents feather anatomy in a lineage that had never been sampled, which is a real advance. It does not demonstrate that feathers caused the survival pattern, and the team does not claim it does. The paper also notes that without additional fossils, the researchers cannot say how the primitive feather types affected hesperornithiform behavior.

A Standing Invitation to Other Museums

The practical next step falls to collections managers and curators rather than field crews. O'Connor described the paper as a call to action, urging other researchers and museums to run computed tomography scans on coprolites already sitting in their drawers.

For readers, there is a smaller takeaway worth holding onto. O'Connor noted that many teams from many museums have worked Hell Creek for 110-plus years without finding a feather there, and the specimen that produced this one looked like an unremarkable brown pebble. The fossil with the exposed feather is now on permanent display at the Burke Museum as part of its "Drama at the K-Pg" exhibit. The research was funded by donations to the Hell Creek Project.

What Readers Want to Know

What was actually found? Multiple well-preserved feathers, plus tiny gar scales and bird leg bones, inside a fossilized dinosaur dropping from the Hell Creek Formation in eastern Montana.

Which dinosaur produced it? Researchers do not know. Size and contents suggest a large predator, with Tyrannosaurus rex and Nanotyrannus named as candidates, but the animal has not been identified.

What bird did the feathers come from? A hesperornithiform, an extinct aquatic flightless diving bird. These are the first feathers ever identified from that group.

Does this prove why birds survived the extinction? No. The researchers propose that feather type and molting patterns may have contributed to which birds survived. An outside expert said more fossils are needed to test it.

Where was the study published? Current Biology, on September 10, 2026, with Jingmai O'Connor of the Field Museum as lead author.

Why does the discovery method matter? Coprolites had not been treated as a source of preserved soft tissue. The team is urging other museums to scan specimens already in their collections.

Can the public see the fossil? Yes. The specimen with the exposed feather is on permanent display at the Burke Museum in Seattle as part of the "Drama at the K-Pg" exhibit.